1. Field of the Invention
The present invention relates to protection of a second pole tip during fabrication of a write head and more particularly to protection of a track width defined by first and second side walls and the thickness of the second pole tip during construction of metallic components of the write head such as lead layers and studs.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, a slider with read and write heads which is supported by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic bits to and reading magnetic bits from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a write coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a nonmagnetic gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. A write current conducted to the write coil layer induces a magnetic field into the pole pieces that fringes across the gap between the pole pieces at the ABS. The fringe field writes information in tracks on moving media, such as in circular tracks on a rotating disk. First ends of first and second leads are connected to the write coil and second ends of the first and second leads are connected to first and second studs that are exposed at a surface of the slider for connection to a source for producing the aforementioned write current.
The read head includes a sensor for sensing signal fields from the rotating magnetic disk. The signal fields from the rotating disk cause changes in the resistance of the sensor. First and second leads are connected to the sensor for conducting a sense current through the sensor so that the resistance changes cause potential changes in a sense current circuit which can be processed as playback signals. The sensor and the first and second leads are located between first and second read gap layers. The first and second read gap layers are located between first and second shield layers in a piggyback head or between a first shield layer and a common second shield first pole piece layer in a merged magnetic head. The first and second leads of the sensor are connected to terminal leads which are, in turn, connected to studs that are exposed at the surface of the slider for connection to a source for producing the aforementioned sense current.
There are two types of magnetic write heads, one of these heads being a standard write head and the other being a stitched write head. In the standard write head the second pole piece is a single layer whereas in the stitched write head the second pole piece comprises first and second layers. The first layer is located in a pole tip region of the head and the second layer is located in yoke and back gap regions of the head. The pole tip region is defined as the region between the ABS and a flare point (point at which the second pole piece first commences to widen after the ABS), the back gap region where the second pole piece is connected to the first pole piece and the yoke region which is located between the flare point and the back gap. In the stitched head a bottom portion of the yoke portion of the second pole piece layer is connected to a top portion of the pole tip portion of the second pole piece layer. In the standard head the second pole piece layer is constructed after formation of the insulation stack with one or more coil layers embedded therein and in the stitched head the insulation stack with one or more coil layers embedded therein is constructed after construction of the pole tip portion of the second pole piece layer. The yoke and back gap portions of the second pole piece layer are then constructed after construction of the insulation stack. One advantage of the stitched head is that the second pole tip portion can be constructed by photolithographic techniques without reflective notching from a seed layer on the insulation stack since the second pole tip portion is constructed before the insulation stack.
Research efforts are still intense for increasing the storage capacity of magnetic disk drives. The product of track width density and linear bit density equals areal density which is quantified in bits per square inch of the magnetic medium. Linear bit density is the number of bits per inch along a length of the track whereas track width density is the number of tracks written per inch along a width of the magnetic medium. Because of the directional rotation of the magnetic disk the second pole tip portion is the last pole tip to pass by the rotating track. Accordingly, the distance between the first and second side walls of the second pole tip portion determines the track width density of the write head. Efforts are now submicron track widths. It is expected with a track width of 0.75 .mu.m the areal density will be 10 gigabits per square inch, a track width of 0.5 .mu.m will provide an areal density of 20 gigabits per square inch and a track width of 0.29 .mu.m will provide an areal density of 40 gigabits per square inch. As the track width gets smaller the standard deviation or sigma (.sigma.) must also be smaller. The sigma is dependent upon many factors such as the photolithographic techniques employed for fabricating the second pole tip portion. In photolithographic patterning a layer of photoresist, the photoresist layer is spun on the wafer, the photoresist layer is exposed to light in areas where the photoresist is to be removed (assuming the photoresist is a positive photoresist), the photoresist layer is subjected to a developer which removes the photoresist exposed to the light, a write head component is then electroplated in the opening of the photoresist, and the photoresist is removed by a stripper. The accuracy of the track width of the second pole piece portion made by this technique depends upon the accuracy of the alignment marks on the wafer, uniformity of the resist coating, focal plane of the photo tool exposing the photoresist to light, uniformity of the illumination of the light and uniformity of development of the photoresist after being exposed to the light. The sigma is also dependent upon the degree of alteration of the first and second side walls by subsequent processing steps such as fabrication of metallic components of the write head, which will be discussed in more detail hereinafter. An existing goal is that the 3 sigma be no more than 10% of the designed track width. For instance, for a 40 gigabit density write head the 3 sigma should be no more than 30 .ANG. which is approximately 10% of a track width of 0.29 .mu.m. As indicated hereinabove, the metallic components of the write head are made by electroplating. The metallic components of the write head are the first pole piece layer, the coil layer, terminal leads to the write coil layer, leads to a read sensor, when the write head is combined with a read head, terminal leads to the read sensor leads and studs to the terminal leads which are exposed at a surface of the head assembly for connection to processing circuitry. All of these metallic components are constructed with photolithographic patterning. Before the photolithographic patterning, however, a seed layer of copper (Cu) is sputter deposited on the wafer to provide a return path for the electroplating. Before the seed layer is sputter deposited the wafer is sputter etched so that the wafer and all exposed components thereon have a clean surface for the seed layer. After the photolithographic construction the photoresist is removed, as described hereinabove, and the wafer is ion milled to remove all of the exposed seed layer.
Unfortunately, the aforementioned sputter etching and ion milling steps can seriously alter the track width of the second pole tip portion of the second pole piece layer. While the sputter etch cleans the surface of the wafer for the seed layer it also removes a portion of the first and second side walls of the second pole tip layer, reducing its track width as well as some of the thickness of the second pole tip layer. When ion milling is employed to remove the exposed seed layer after photopatterning of a metallic component the ion milling also removes a portion of the first and second side walls of the second pole tip portion to further reduce the track width as well as more of the thickness of the second pole tip layer. Ion milling also has a second negative aspect on the second pole tip. As the copper (Cu) seed layer is being removed by ion milling a portion of the copper (Cu) is deposited on the first and second side walls of the second pole tip which is referred to in the art as redeposition or redep. Since this redeposition is copper (Cu) it will be exposed at the ABS when the ABS is formed by lapping which is a grinding process. Unfortunately, the copper (Cu) and nickel iron (NiFe) of the pole pieces set up a galvanic cell which can cause serious corrosion of the sensitive elements of the write head at the ABS. This corrosion can destroy the write head.
Metallic components constructed after the construction the second pole piece layer in a standard head are terminal leads and studs, whereas metallic components constructed after construction of the second pole tip portion of the second piece layer in a stitched head are the write coil layer, the terminal leads and the studs. Accordingly, the pole tip portion of a stitched head is subjected to more alteration than a standard head.